Abstract: In total, 58 overwintered Maculinea nausithous (BERGSTRÄSSER, 1779) larvae were found in nests of Myrmica rubra (Linnaeus, 1758) from three sites in West Hungary. These results confirm that M. rubra is, in general, the host ant of M. nausithous. Twenty-eight larvae of M. nausithous and eight larvae of M. teleius (BERGSTRÄSSER, 1779) were found in a single M. rubra nest, which is a huge density for predacious butterfly species.